Aqua Tower: A Landmark Addition to the Chicago's Skyline

Chicago's Aqua tower with its rippling facade and vast green roof is the tallest building in the world to be designed by a woman. Ar Jeanne Gang, a forty-eight-year-old Chicagoan, had figured out a way to make a silky line with a fairly conventional rectangular glass slab, and then transformed it by wrapping it on all four sides with wafer-thin, curving concrete balconies, describing a different shape on each floor. More than having a pretty face, special emphasis has been given on innovative green design and energy-efficient features in the structure such as heat-resistant and fritted glass, rainwater collection systems, and energy-saving lighting systems which address environmental concerns on a large scale.

The 86-storey mixed-use Aqua tower includes a hotel, apartments, condominiums, parking and offices. Unlike a tower in an open field, new towers in urban environments must negotiate small view corridors between existing buildings. In response to this, the Aqua Tower is designed to capture particular views that would otherwise be unattainable. A series of contours defined by outdoor terraces extends away from the face of the tower structure to provide views between neighboring buildings. These outdoor terraces, cantilevered up to twelve feet, differ in shape from floor to floor. The terraces inflect based on criteria such as the view, solar shading and size and type of dwelling. When viewed together, these unique terraces make the building appear to undulate, presenting a highly sculptural appearance that is rooted in function. Aqua creates a strong identity through its architecture and has become a landmark addition to the Chicago skyline.

The name 'Aqua' was assigned to the building by the developer Magellan Development Group LLC. It fits the nautical theme of the other buildings in the Lakeshore East development, and is derived from the wave-like forms of the balconies; the tower's proximity to nearby Lake Michigan also influenced the name.

Located on the 200 block of North Columbus Drive, and surrounded by highrises, Aqua rises from a podium on the 179,946 square feet site near Millennium Park. The architect Jeanne Gang has given swirling architectonic form to this 1.9 million square feet structures' envelop while working with the building's rectangular footprint. As a mixed-use structure that contains 55,000 square feet (5,100 square meters) of retail and office space, in addition to 215 hotel rooms (floors 1-18), 476 rental residential units (floors 19-52), and 263 condominium units & Penthouses (floors 53-81), Aqua's entrances serve a variety of users and residents. Canopied walkways lead visitors to the building's main entrance while two grand public stairs bring pedestrians from Upper Columbus Drive down to a park at grade level, providing access to Chicago's downtown area and lakefront. The tower also connects to Chicago's extensive underground pedway system, linking users and residents to restaurants, retail, cultural activities and jobs in the Loop and on the Magnificent Mile. Additional consideration was made when designing the tower's garage exits below grade to minimize congestion at pedestrian levels. To further reduce traffic and confusion, the garage's three levels have different access points that correlate to the tower's specific uses and users.

The outdoor terraces which are cantilevered up to 4m (12ft) and have a depth of 23cm (9in), thins out towards the edge of the cantilever to assist with water drainage. The challenge of constructing unique floor plates was solved by implementing a computerized civil engineering and surveying software program and digital CAD files for inputting the coordinates of each unique slab to a robotic station used onsite. This system was used to set in place light-gauge steel plate edge-forms according to the contours. After the concrete had set, these steel forms were removed and easily reshaped according to the contours of the next level. The result is a highrise tower particular to its site that allows residents to inhabit the facade of the building and the city at the same time. Early and close collaboration between architect and builder, as well as the use of contemporary digital tools, allowed the variation in the shape of the floor slabs to be achieved without increasing the building's construction timetable.

Aqua Tower was recognized as a finalist in the 2010 CTBUH Awards Program. According to Mun Summ Wong, CTBUH 2010 Awards Juror, and WOHA Architects "The differential cantilevering balconies on Aqua transform a standardized glass box into a sublime amorphous form."

Sustainable Designs

Sustainability was an important factor that was considered in Aqua's design. Among building's notable features is the green roof terrace atop its plinth-which at 80,000 sf is one of Chicago's largest-that contains an outdoor pool, running track, gardens, fire pits and yoga terrace. From below, Aqua's plinth navigates the site's complexity by spanning over pre-existing elements, such as an electrical substation, and by aligning with existing infrastructure, including an adjacent three-level roadway. The plinth physically connects pedestrian areas with stairs and elevators linking street level to park level and the lakefront.

The tower's east–west orientation maximizes its winter solar performance. Its balconies extend further on the southern façade to provide shading, reducing solar exposure in summer and allowing passive warming in winter.

In addition to low-E coatings on all glass, the design team modeled seasonal sun patterns to identify remaining areas of glass that needed higher performing glazing to increase energy efficiency throughout the tower. Glass on the east and south façades are reflective in areas without a protective balcony, while glass facing west has a tinted coating that improves its shading coefficient. In total, Aqua employs six different types of glass: clear, tinted, reflective, spandrel, fritted and translucent, the placement of which is determined by the orientation and function of interior space. Fritted glass is used and combined with handrail design to minimize bird strikes.

"Aqua Tower was shaped by an organic, site-specific design process. Rather than starting out with the goal of creating an icon, we let the climate and views shape the building, weaving it into its surroundings and treating the building and its environment as interconnected not separate. Even though it may appear to be formally expressive, it is equal parts data and imagination" –– Jeanne Gang, Design Principal Architect.

In addition, detailed wind tunnel studies were also done to confirm the performance of the structure under high winds. Initially, it was thought that a supplemental tuned mass damping system may be required to appropriately manage the effects of the wind on occupant comfort. However, during the testing, it was discovered that the undulating slab edges disrupted or "confused" the flow of wind around the tower, effectively reducing the wind demands, and this, combined with the effectiveness of the structural design, eliminated the need for a supplemental damping system.

Inside the dwelling units, the architects selected materials and equipment with sustainable features such as renewable and recyclable bamboo for the floors, plumbing fixtures including toilets, faucets, and showerheads that cut down on water use, plus Energy Star-rated appliances.